On Oct 23, 2006, at 4:22 PM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Oct 23, 2006, at 12:07 AM, pentalab wrote:
Tom's problem with dipmeters was when one showed that grid-
resonance Decreases in frequency when a grid is grounded with
heavy duty Cu straps instead of caps (SB-220, TL-922. L4B)
### IT does decrease.... by just 1 mhz if I remember. What I
don't understand is.... why does stability improve with grids
strapped directly to? chassis ??
It may and it may not. Moving one resonance a bit may appear to be
a sure cure, however, removing the perforated cover from a Henry
2K-4
will usually make it more stable but in my experiences parasitic
oscillations are inheriently on the ragged edge, so it's easy to be
deluded into thinking you made a slam-dunk by making one change
and seeing no fireworks during a few minute test.
##### well how about 3 doz L4B's, SB-220, SB-221, TL922,s...
that all had their grids directly grounded....... and have been
like that, running flawlessly for at least 4 -5 years now ???
They all have stock suppressor's in em too.
** ______
I'd still grnd the
grids directly.... just cuz the drive requirements drop by an
easy 20-25 watts.
That the 2 x 600pF of grid bypass on the pair of 3-500Zs in a 922,
L4- B or SB-220 dissipate 20 - 25w is hardly likely.
### agreed. The point here is the drive power requirement DOES
drop by 20-25 watts. I measured several of em with bird
wattmeter's.... that had been recently calibrated. During the b4
and after test.... it's always the same on a L4B.... exactly 22
watts LESS drive... WITH the grids directly grnded.
### MY tech buddy's with the SB-221 and 220 and the fellows
with the TL-922 reported between 20-25 watts LESS drive
required. The wattmeter's don't lie. And that test has
been done countless times by other's too. The TX imd improves
a lot too. That NFB is non existent with the 3 x 200 pf caps
in place. Run the xcvr at 20-25 watts LESS output.... and the
xcvr's IMD will clean up too...... total imd is way down. Try it
urself.
### Lemmee ask u this Rich..... IF u were gonna build a HB 2 x 3-
500Z linear from scratch... would u use the 3 x 200 pf caps [ or
any othwer value] or not ??????????????????
I would use: 1500 - 2000 pF total per socket consisting of three
different values per each, a grid fusing element, a FWD/FWB
switchable PS, and I would use a glitch R, followed by an 8160.
later... Jim VE7RF
Yahoo! Groups Links
R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
